When installing communications cables in underground conduits, it is common practice to supply gas at super-atmospheric pressure to the interior of the cable with a view to avoiding any danger of leakage of ground water into the cable interior through its sheath. Additionally, the maintenance of pressure within the sheath is an indication that the latter has not suffered damage during installation. Pressurization of cables during installation is presently accomplished by applying end caps to the ends of the cable to seal the latter, and applying gas under pressure through valves incorporated in the sealing caps. Where the cable is to be pulled into its final location, one of these end caps will be equipped with a pulling eye and designed to transmit tensile forces to the cable. In order to transmit such tensile forces to the cable, it is known to provide end caps in the form of a tubular sleeve which fits over an end of the cable, the sleeve being closed at one end by a closure having an external pulling eye and a spigot which extends axially of the sleeve. When the end cap is fitted, the spigot is driven into the end of the cable, and the sleeve is then circumferentially crimped so that the cable conductors are compressed against the spigot. The spigot is shaped with at least one enlargement intermediate its length so as to help retain the conductors and and distribute the tensile loadings between the spigot and sleeve.
A disadvantage of this arrangement (which may also be used as an end cap at the other end of the cable, in which case the pulling eye may be omitted) is that the crimping of the sleeve onto the cable end compresses the conductors together so firmly that the passage of pressurizing air from a valve in the end cap to the interior of the cable is restricted or prevented. One proposal for overcoming this problem is found in U.S. Pat. No. 3,989,400 issued Nov. 2, 1976 to Smith et al, in which the valve in the end cap is arranged so as to introduce air into an axial bore extending the length of the spigot. This solution is less than ideal. The longitudinal drilling of the spigot is an expensive operation, and the spigot must then either be attached to the end cap by a threaded or other mechanical connection, as shown, so as to achieve communication with the valve, or the necessary drilling must be carried out after the spigot has been welded to the end cap. These requirements add greatly to the cost of producing the device, whilst the longitudinal bore in the spigot inevitably reduces its strength. Furthermore, there is a danger that the downstream end of the bore may be obstructed by cable conductors, thus again restricting the rate at which air can be introduced into the cable.
Another prior art proposal is to be found in U.S. Pat. No. 4,002,817 issued Jan. 11, 1977 to DeGrado. In DeGrado, a small bore tube is provided coaxial with the sleeve for the injection of air, but this tube takes no part in the transfer of tensile forces between the pulling eye and the cable, its sole purpose being to act as a gas conduit.